It is generally known to use an annular or ring seal, e.g. in the form of a stopper bushing, to seal a connecting cable, composed of multiple conductors, in the entry section of an electrical plug connection. This is intended to prevent moisture from seeping, along the outer surface or cladding of the connecting cable, into the plug connection.
If the plug-connection-remote interior section of the connecting cable is located in a moisture-filled space, there can result an undesirable transport of moisture within the connecting cable, along the conductors, which cannot be stopped merely by an annular seal around the connecting cable.
In such a case, one employs a more elaborate and costly individual conductor seal, as described in German published application DE-OS 35 45 223 and corresponding U.S. Pat. No. 4,722,696. Here, the connecting cable is "feathered" at the electrical plug connection into the individual conductors, and each individual conductor is provided with an annular seal.
According to this costly method, it is usual to provide a seal on the housing of the plug connector, for example in the form of an O-ring on a cylindrical portion of the housing, in order to seal the plug and socket against the external space, which is under atmospheric pressure.
By means of this outer seal, on the one hand, and by means of the sealing of the individual conductors, on the other hand, an air volume is defined in the plug connection. Temperature changes, and ambient air pressure changes, mean that this trapped or enclosed air volume is alternately at overpressure or underpressure, compared to the ambient air. When the enclosed air volume is at underpressure, and water is present in the space surrounding the plug connection, micropores in the outer seal and other seal result in undesirable aspiration of water into the interior space of the plug connection. This must be prevented or at least minimized.